Manual

8of16 MN301040 RevB
GETTINGSTARTED StepSeven
Pressure transmitters are designed to be submersed within the application fluid.The
transmitters can either rest along the bottom of the tank or be suspended at any
desired level within the tank.Please note that the physical location of the level
transmitterwillindicatethelowestlevelofmeasurementwithinthetank.Forexample:
mountingthetransmitter1footfromthebottomofthetank,thenthelowestreading
ofliquidwillbe1footfromthebottom.

HowtoconvertPressureintoLiquidHeight?
PressuretransmittersarealldescribebythepressurerangeandnotbyLiquidHeight.Toconvertpressureto
LiquidHeight,usethefollowingratio:
1psi=2.31feetofwateror1psi=0.704metersofwater
Therefore,a15psitransmitterwillhaveaLiquidHeight=34.65feet(10.56m):
15psix2.31’/psi=34.65’or15psix0.704m/psi=10.56m
With the above ratio, you can always find the Liquid Height or water column
(wc)ofanypressuretransmitter.
Howtoselectthecorrectpressuretransmitter?
The objective is to use a pressure transmitter that will cover the entire range of the application.If the liquid
heightofthetankisabovethetransmitter’sMaximumLiquidHeight,thenthesensorwillnot beabletoread
thelevelofafulltank.Comparethetank’sPressure@Full againstthetransmitter’spressuretoselectasensor.
Tocalculatethetank’sPressure@Full,usethefollowingformula:
RequiredMaximumPressure=[FullTankHeight(feet)xSG]/2.31(feet/psi)
RequiredMaximumPressure=[FullTankHeight(meters)xSG]/0.704(m/psi)
Toselectthecorrectpressuretransmitter,followthestepsbelow:
 MeasuretheHeight@FullTank(infeetormeters).
 DeterminetheSGfortheliquid(ifthecustomerdoesnotknow,checktheMSDSsheet).
 UsetheformulaabovetocalculatethePressure@Full.
a. Ex:A40’tankwithaliquidmediaSGof0.9hasaPressure@Fullof15.58psi.
b. [(40’x0.9)/2.31’/psi]=15.58psi
 SelectapressuretransmitterwithapressuregreaterthanorequaltothePressure@Full.
a. Intheexampleabovefora40’talltankwithaSG=0.9,youneedapressurerangegreaterthan
orequalto15.58psi.
b. Using a sensor with a pressure range of 20 psi provides a Maximum Liquid Height of 51.33’,
whichwillreadtheentirerangeofthe40’talltank.
c. Using a sensor with a pressure range of 15 psi provides a Maximum Liquid Height of 38.50’,
whichisshortby1.5’.
i. Thismeans
thatthesensorwilloutput20mAat38.5’ofliquidandthetop1.5’ofliquid
willnotbemeasured.
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